I will answer this question with a question of my own: why would the crow in the above picture be white when all other crows are black? White crows exist, but they are extremely rare. Most planetary bodies are spherical. According to Flat Earth Theory they are smaller and much closer to the surface of the Earth and orbit above its surface. But this does not entail that ALL planets, including Earth, are spherical as well. As discussed elsewhere on this site, a planetary body with an upward facing surface is alone capable of supporting life as we know it. Any organism that does not directly attach itself to the ground would eventually fall off the bottom of a spherical planet.